1. Field of the Invention
This invention pertains to pressure vessels and particularly to features of high pressure blowout preventers that allow for the reduction of profile and/or reduction of weight as compared with conventional blowout preventers, without sacrificing or reducing the operating parameters.
2. Description of the Prior art
Blowout preventers are employed in oil and gas wells as safety devices to ensure that the well bore is closed off in the presence of unexpected high pressures developing down hole. Blowout preventers operate to not only assure personnel safety, but also to prevent tubing and tools and even drilling fluids from being blown out of the well when a blowout threatens.
There are many different kinds of blowout preventers, but one of the most popular types employed in offshore applications where the highest downhole pressures may be encountered is the ram blowout preventer. A ram type blowout preventer is essentially a specialized type of valve that closes off the wellbore through the use of operational rams positioned transverse to the wellbore and which meet at the center when closed to close off the hole. The faces of the rams are equipped with large rubber packers suitably shaped to close around tubing, drill pipe, casing or on each other when the hole through the blowout preventer is open. When the hole through the blowout preventer is not open then when the rams close, they close off the annulus between the outside of the pipe in the hole and the wellbore. The opening and closing motivating force to the rams is suitably controlled and applied hydraulic fluid pressure.
Ram type blowout preventers meet all kinds of drilling applications and can be used on the land, on offshore platforms and subsea.
The principal housing parts of a blowout preventer are its body and its bonnets. The body is the center part of the housing that includes a center, vertical opening for alignment with the borehole and transverse guideways for permitting ram operation as described above, the guideways being on two opposite sides of the center opening. Since the rams move an appreciable distance in and out, the housing is extended on either side contiguous with the guideways into guideway extensions located in bonnets. Thus, there are two bonnets located on either side of the body.
Bonnets are typically bolted to the body using a plurality of bolts that bolt a flange on the bonnet to the body. The bolts conventionally are pressure torqued to minimize pressure leaks between the body and the bonnet, are located so as to mostly surround the guideway extension, and are located in multiple circular rows. Thus, it is apparent that to remove such a bonnet, pressure tools are required to remove the many highly torqued bolts. It is not uncommon for such removal to take 20-30 minutes. The multiple bolt rows or partial rows and by mostly surrounding the extension guideway of the bonnet necessitate wide flanges. Thus, the heights and the widths of the body and bonnet flanges are appreciable.
It is conventional in some very high pressure applications to stack blowout preventers one above the other. It is known in the prior art to include a stacked arrangement utilizing a single body with two or more sets of guideways, each guideway set is associated with its own pair of bonnets. Such bonnets have been attached as described above, thereby reducing the overall height to be somewhat less than two completely separate blowout preventers. However, the dimensional requirements of the bonnets are the same as discussed above.
Another possible space problem involves how the bonnets are mounted for easy access. Bonnets that are only bolted on are not easy to handle when disassembled. They are heavy and they are difficult to hold in position while the connecting bolts are reinserted and tightened. To alleviate these problems, a hinge has been used to hold a bonnet to the body while the connecting bolts are removed. Although satisfactory in many installations, it is necessary to anticipate the conditions of crowded installations so that the hinge bolt holes on the body can be drilled and tapped on the correct side for accepting the hinge. Otherwise, there may not be enough room to hinge the bonnet properly for ready access.
As previously mentioned, the rams of the blowout preventer are hydraulically operated. The piston drive end of a ram is located in a guideway extension or cylinder portion thereof located in the bonnet. Depending on whether the piston is being driven to close the ram or open the ram, hydraulic fluid is directed to one side or the other of the piston. At the same time that motivating fluid is applied to one side, the other side of the piston has to be ported for evacuating the fluid previously applied thereto. Application of fluid to and from a ram type blowout preventer traditionally is to and from "open" and "close" ports in the body and, from there, through passages in a hinge to the applicable passages in the bonnet. If there is a hydraulic problem, all of the above passageway possibilities exist, including possible problems in the body, which is the least removable or replaceable component of the entire blowout preventer assembly of parts.
In the fluid hinge itself, high power fluid is applied one way or the other depending on whether fluid is being applied to close or open a ram. This applies pressure on the hinge that could cause leakage except for the fact that a balancing system of components are used to insure against leaks and to maintain balanced pressure on the hinge regardless of the applied hydraulic fluid pressure direction. The prior art balancing system typically has utilized two mechanical springs and one or more sealing subs.
Typically, a ram operates within a sleeve present in the guideway extension of the bonnet. Fluid to the "close" side of the piston head of the ram is directed in such a system between the sleeve and the guideway extension. It will be noted that by eliminating such a sleeve and including a passageway for the closing hydraulic fluid within the housing of the bonnet, valuable reduction in overall size of the bonnet can be achieved vis-a-vis the prior art.
It is therefore a feature of the present invention to provide an improved high pressure ram-type blowout preventer that utilizes having a sealing ring around the hydraulic pistons of the rams to reduce the number of bolt holes necessary to connect the body to a bonnet and therefore reduce the weight and profile of the overall blowout preventer without reducing its operating pressure characteristics.
It is another feature of the present invention to provide an improved stacked ram-type blowout preventer that has a simplified bolting connection arrangement to lower the weight and profile requirements therefor compared with a comparable stack of the prior art.
It is yet another feature of the present invention to provide an improved ram-type blowout preventer that has a universal hinge plate that permits the location of hinges on either side of its body for hinging the bonnets to thereby avoid difficulties that would otherwise be encountered because of limited space availability.
It is still another feature of the present invention to provide an improved ram-type blowout preventer that uses a universal hinge plate with internal hydraulic passageways to facilitate maintenance by avoiding having such passageways in the body of the blowout preventer.
It is yet another feature of the present invention to provide an improved ram-type blowout preventer that employs passageways for the application of hydraulic fluid only in the housing of the bonnet and not between a sleeve and a guideway extension to simplify the arrangement of passageways compared with the prior art to thereby reduce the overall size of the bonnet.